Abnormal Shells and Piracy
by E. R. Cross
Some of the most rewarding experiences in recreational diving, whether with scuba or free-diving, are the underwater encounters;from sharks to the tiny marine life that may be drifters, swimmers or bottom dwellers. Divers will ultimately find all sizes of marine life equally exciting and certainly different. As they gain knowledge and experience about ocean life, rewards become greater. This will be true for the student of marine life as well as for wreck divers and underwater photographers. The hunter-gatherer engaged in spearfishing will also benefit from the accumulated knowledge.
In a recent issue of Skin Diver Magazine, Technifacts mentioned the possibility of melanism and rostration in shells of mollusks inhabiting polluted waters. In particular, reference was made to gastropods inhabiting steel artificial reefs. Readers were curious about the meanings of melanism and rostration. Generally, but not always, these conditions appear separately but may be found together in specimens of some gastropods. Albinism also occurs in mollusks.
The shells in the illustration are specimens of Cypraea fimbriata. It is a small cowry found throughout the Indo-West Pacific. Normally the shell is smooth, ovate and about 10 to 12mm in length. The color is usually pale blue-gray with light brownish spots and two weak brown bands across the center of the dorsum, as shown in the two specimens in the middle of the illustration.
The shells illustrated were collected by R. Pierson of Noumea. The two center shells are about twice normal size but nearly normal in both color and form. The upper two pairs of specimens are albino shells. The lower two pairs of shells are both melanistic and rostrate.
In the New Guinea area, the tailings from many open mines are sluiced or are allowed to slough through into the surrounding ocean. These conditions also exist in several areas of Fiji. Melanistic and rostrate shells are collected in these areas. A form of discoloration appears in certain conditions known as metallic melanism or, in the case of association with silver, argyric melanism (argyric refers to silver). In the case of steel vessels, the discoloration is referred to as iron oxide melanism.
My worry, as expressed in the prior Technifacts, was whether metallic melanism, whatever the form or cause, is harmful to the mollusk. Also, are these tailings harmful to other marine life.
It is difficult to accurately define melanism and rostration since they are used with different context in various sciences. In a science dictionary, melanin is defined as any group of brown or black pigments occurring in plants or animals. In a medical dictionary, the same word is defined as the dark, formless discoloration of skin, hair and other coatings. It is produced by polymerization of oxidation products and contains carbon, hydrogen, nitrogen, oxygen and often sulfur compounds. Melanism is an excessive pigmentation or blackening of the skin or other tissues. Or it may be a discoloration produced by the pigments found in chemical solution in the water in which the mollusk is found.
Rostration is also difficult to define accurately in mollusks. Rostration is natural in some shells. In others it is an abnormal condition. The term is also applied to some shells that are rostrate owing to repaired damage, and to a shell damaged owing to physiological or environmental conditions.
In some gastropods, the grooved extensions of shells range naturally beyond what might appear to be the normal end of the shell. Early writers defined this as being rostrate. Some such shells are scientifically named rostratum (e.g. Cerithium rostratum). Usually this shell extension protects the fleshy siphon when it is extended and functioning normally. In modern description of such shells this normal growth extension may be referred to as a siphonal canal or as being beaked rather than being rostrate.
Other deformities of the shell owing to abnormal metabolic processes will probably be termed rostration. Repairs to physical shell damage inflicted by predators such as a crab or fish may also result in a rostrate shell. Most shells can repair damage that does not prevent normal functioning, provided the animal part of the mollusk is protected from further damage.
Some mollusks also suffer from albinism. Albinism is the absence of pigment in the skin, hair or other covering such as the shells of the mollusks. This may be genetic and is probably a rarity. In certain polluted areas, I have found this condition more common. Other mollusks having aberrant colors and distorted forms were collected in different areas having different kinds of pollution. These will be illustrated and discussed in future Technifacts.
I am sure readers have observed marine fauna during their dives. If you have questions, comments or additional information about any aspect of your sightings, Technifacts will be glad to exchange information with you. Write to E. R. Cross, c/o Technifacts, Skin Diver Magazine, 6420 Wilshire Boulevard, Los Angeles, CA 90048-5515.
Piracy on the High Seas
Where did all the pirates go? Some got wealthy and retired; comfortably, I might add. A few were hung from yardarms. Some were washed or thrown overboard. There were also those who jumped overboard to avoid a dreadful end to their nefarious lives. Also, there are more pirates in todays maritime world than at any time before. According to a recent study, there were 90 piracy incidents in 1994. Piracy activities increased to 226 cases in 1996. This study indicated the actual cases of piracy may be twice that amount since ship owners fail to report many cases. It takes too long and is too expensive to have piracy cases investigated.
The location of the largest number of piracy attacks remains almost the same as in the early years. Particularly dangerous areas are in the Mediterranean off Albania and Libya and the South China Sea.
Possibly the pirates are aware that little can be done about the problem since most attacks are in territorial waters; a UN task force cannot normally take any action.